Complicated
by Veleum
Summary: It was hard enough, leaving his village before he was given a decent sexual education, but to learn about the different secondary genders from Kisame of all people was not Uchiha Itachi's idea of a fun time. And yet, here was the all feared mist ninja patiently explaining everything he needed to know. AKA a coming of age story where Itachi goes through the joys of presenting.
1. Chapter 1

If there was one thing that Kirigakure was well known for, it was the fact that they produced some of the most dominant Alphas within all of the different hidden villages. It was due to them, that scent blockers and special suppressants had been created for all genders of all types, as well as special jutsu that was used on an Alpha in rut, or an Omega in heat.

Being a young adult before he left, and also being part of a clan well known for being some of the most savage alphas ever known, Kisame had a very thorough knowledge of what needed to be done with young adults and teenagers who first presented. His knowledge turned out to be very helpful in lieu of the younger members of the Akatsuki, once he defected.

It was especially the case when his partner was assigned to him, a 13 year old Uchiha, another clan well known for producing both strong Alpha's AND Omegas.

Pein knew he could trust the young boy with Kisame, who could protect him from others, and himself, when he couldn't do so himself, because unlike Kirigakure - it seemed as though Konohagakure took a different path on teaching the secondary genders.

Or rather, because Itachi had graduated so young, he never got taught _anything_ except the basics.

This, of course, left Kisame with the incredibly awkward job of teaching a now 14 year old Itachi everything he needed to know for when he presented. It had taken that long for the two of them to trust one another, though the Kiri-nin knew that there was much left to discuss, and much that the two of them were still hiding from one another.

It was to be expected. They were ninjas, and ninja were masters of secret keeping from them all.

Thus, there they were on a mission, as per normal, when Kisame had stopped to purchase some items for himself. As was normal, he took suppressants to prevent his already highly developed animal tendencies from causing issues. However, while he was making his purchases, he noticed a commotion outside.

He came out to find several terrified alpha's (by the smell of them) running away from a very pissed off Itachi, to which he could only ask, "what just happened?"

Red eyes glared at him from under the straw hat, "they apparently wanted me as their mate because I 'looked like a weak, pretty little thing'."

Kisame almost took a step back from the way the red eyes spiraled, but he knew that Itachi wouldn't use his Sharingan against him without very good reason.

"Well, that's disgusting," the former kiri-nin commented, said disgust laced in his voice. Itachi was _14._ Those alphas had to be at least in their _twenties._

"They smelt disgusting."

 _That_ interested Kisame; as far as he knew, only alphas and omegas could pick up on scents, unless they were very strong, or very repugnant. The older ninja was inclined to think they were the kind who stunk, and didn't take suppressants like the majority of the decent people of the world.

He might be a criminal, but he had _class._

"Well, I got what I needed, let's head back," was all Kisame said in response to the statement, and they headed back to the hotel they were staying at for their mission.

* * *

Later that night, they had returned to their hotel stinking of blood, which was not an uncommon thing for a ninja to return back from, and after their showers, Kisame walked out of the bathroom in one of the inn's robes to find Itachi staring intently at the boxes the other ninja had purchased earlier that day.

"Can't read it?" he joked, earning him a glare.

"I have never seen Alpha suppressants before."

"Oh," the taller man merely came over and settled on the other side of the small table, "want me to walk you through em?"

"Hn."

Kisame took that as a yes, and picked up the first box, "this is a scent cancelling soap - you must've seen these before in Konoha, right?"

A nod.

"It's not just for alphas - omegas use them too, to avoid being harassed, mostly," he shrugged, "though, most of the omegas in Kirigakure aren't ones you'd want to mess with anyway," Kisame snickered, and opened the box so Itachi could smell the soap, of which he did with interest, "not as many alphas use them, but I do. Otherwise I'd draw too much attention to myself."

"I thought you were self conscious about your appearance?" Itachi had no filter at age 14, Kisame had long since discovered, and he scowled at the teen.

"As a _ninja,_ you brat. Now shall I go on?"

Itachi merely set the soap down and returned his attention to the older man, to which Kisame huffed, and continued by picking up the second box.

"Scent spray, in case I'm not near a bath and have worked up a heavy scent, same principal as the soap," he set the box aside, and picked up the last, largest box.

"Pills, for the suppression. Stops me going into rut and lessens the instinctual part of the Alpha gender. Basically," he continued, as he noticed Itachi's slight change in facial expression that he understood to mean he was confused, "if I walk past an Omega nearing heat, or in heat, I'm not going to chase after them and rape them."

"Oh," was all Itachi said.

"Suppressions for Omegas stop heats and lessen the effects of an Alpha near them, so depending on what you eventually present as, you ought to take these daily if you present as an alpha or an omega," Kisame explained, and set the box down.

"And if I don't suppress?"

"You'll either go into rut or heat every four months, and be at the mercy of scents and hormones you _probably_ won't like so much," Kisame smirked, "unless you like that kind of thing~"

Itachi merely glared at him and folded his arms, of which the older man snickered at, "I guess not."

It had been no secret that Kisame was an Alpha. Their very first conversation made it clear from his personality alone, as he had attempted to intimidate the child before him. But it hadn't mattered, as though the ice had shattered, they eventually began to get along and gain one another's respect. It was just one of those things.

And so, they went to sleep that night with no further enquiries on secondary genders, though Kisame was obvious to the turmoil it had awoken in Itachi's mind.

* * *

Itachi did not know what he would present as, and the idea of being anything other than a Beta terrified him.

He knew very well that the Uchiha clan was well known for producing powerful ninja of any gender combination, but he also didn't want to have to deal with ruts and heats and heaven forbid, the possibility of impregnating some hapless soul or becoming pregnant _himself._

The lack of knowledge he had about it was something he hated. He had graduated too young to be educated on it, and by the time he had left Konoha, he simply didn't have the time to educate himself on it.

And with the steady stream of missions he had been given, it wasn't as though Itachi had any desire to go and purchase a book on the subject. He considered himself well read, but this?

This was… _embarrassing._

It had only left him with one alternative - ask Kisame, which slowly became less daunting the more time he spent with the man.

Kisame was polite, respectful, and effective in missions, even if his technique stood out glaringly obvious to anyone who knew about his sword. But Kisame also never made him uncomfortable, and it was only after he had been 'harassed' by a group of disgusting men that the teenager deemed it 'necessary' to ask his workmate what the _deal_ was with Alpha's and Omegas.

He was most relieved when the older man both gave him a respectful and simple answer, and also seemed happy to explain the in's and outs of omega and alpha physiology.

Since that day, Itachi had occasionally asked him questions about what being an Alpha was like. He asked him what he knew about Omegas, too, and Kisame was happy to answer. The older ninja also taught Itachi the protection jutsu's for if he ever went into rut or heat, in order to prevent his scent from escaping to… potential 'participants'.

They were at the base when this first came up, for he had wondered why there were four kunai stuck in the walls, one in each corner of the room, with a special tag on it.

"It casts a week long blocking jutsu when active," Kisame answered as he got dressed. Right now, he was just in his underwear, "I use it for when I go into my yearly rut."

Itachi understood that. Once a year since they had been partnered, for three or four days of the year, around the start of September, Itachi would be sent on a solo mission, only to return to a slightly under the weather Kisame who looked like he had fought a bear and won - barely.

"That's convenient…" Itachi could only wonder just how much he had missed in his time away from his village.

"I'm honestly surprised that no one ever explained anything to you," Kisame pointed out as he put his pants on, his gaze on the kunai and a frown on his face, "you should know how to protect yourself."

Itachi glared.

"You _know_ what I mean," the mist ninja deadpanned.

"Hn." Itachi merely turned around, "put on a shirt and let's go."

Kisame merely snickered and did as he was told.

* * *

It was when he had just turned 15 that Itachi began to wonder if he was getting sick. For a few days, he had noticed he had begun to feel hotter, and part of him wondered if he had somehow caught a sexually transmitted disease from a bath, since his loins had also been sore. He confided none of this to Kisame, however he could see the older man shoot him some concerned looks now and then, as though he could sense something off about the teen.

It wasn't until they went out to get some dango and tea that it became obvious that something was amiss. Not only did they attract way too much attention, but there was a group of men staring at Itachi like he was a piece of meat.

He could see Kisame tense up, and even though the hats they wore shielded most of their faces, he could tell the older man was not impressed. Itachi, on the other hand, was feeling dizzy.

"Kisame," he whispered, finally realising that there was no point in hiding his discomfort.

"We should go back," the older man offered softly. The shady trio in the corner certainly looked like they wanted to do _something,_ and it occurred to Kisame what was happening. With a growl, Itachi was startled when he suddenly caught a strong whiff of mint and salty sea breeze wash over him. The men looked like they were about to piss themselves in response.

What… had happened?

The older man finished his tea, slammed his cup down, grabbed Itachi's wrist and tugged him boldly out of the shop after tossing down a couple of coins to pay for their meal.

"Kisame?!" the teenager almost sounded shocked in his confusion, but Kisame looked down at him with a slightly panicked and slightly angry expression once they were in the cooler, night summer's air.

"Are you feeling sick?" he asked.

"What-"

" _Are you feeling sick?"_ the older man demanded more insistently.

For once, Itachi actually felt a jolt of intimidation in his guts, for the first time ever around Kisame, and was acutely aware of the blue man's hand on his wrist.

"Y-yes…"

"Are you hurting down south?"

"Yes…?"

" _Shit,"_ Kisame cursed, and without even bothering to ask Itachi for his permission (of which Kisame was _always_ very good at doing), he grabbed the smaller ninja around the middle and raced back to their hotel room.

"What the hell, Kisame?!" he managed to growl, though he didn't struggle too much in his hold.

"You're _presenting,_ you idiot!" the kiri-nin growled, "you're about to go into a rut or a heat - everyone within a mile radius is about to catch a whiff of you and I'd _rather_ you not be around to see the fall out!"

"I can take care of myself," Itachi all but quietly snarled, his eyes red and spinning.

"No one is denying your ability to fight," Kisame ground out as they arrived, and he didn't even stop to see the receptionist's shocked look as he practically carried the fire-nin up to their shared room, "but tell me that when you're in the middle of either a rut or heat and all you can think about is fucking your opponent!"

Itachi seemed to go silent then, stewing in his own ignorance and wondering how right or wrong the older man was.

Once in their room, Kisame got out four kunai, quickly wrote the same inscriptions he had seen in their own room on each one, and tossed them into the four corners of the room. With fast paced hand movements, he activated the jutsu, which glowed blue and covered the walls in a cold, soft glow before it faded. It was only then that the older man sighed a breath of relief.

"Stay here for the next few days. I'm going to get everything you need," he said calmly and turned to go.

"Wait…"

Kisame paused and turned back.

Itachi had sat on the floor, and now he didn't mask his discomfort. His hat and coat were strewn on the floor, and it was now obvious that he was sweaty, and unhappy. His hands were bunching the futon on the ground that he was sitting on, and for once… he looked _scared._

"What do I… do… here…"

The older nin merely sighed, "your body is preparing itself to go into a heat or a rut. Your hormones are about to go crazy, and you're going to want to fuck everything in sight," he didn't mince words, "so my advice? Turn on the porn channel, teach yourself to masturbate, and try and let your body go through the motions."

It was a good thing Kisame was calm, because Itachi was inwardly _mortified._

"Where are you going?" he asked as a redirect.

"Getting you what you'll need to get through this, and when we know what your secondary gender is, medicine." And with that, the mist-nin left, locking the door firmly behind him.

It was all Itachi could do but follow his partner's advice, and with a great deal of mortification, did he switch to the porn channel, and begin to watch as his hormones claimed him.

* * *

It was a few hours before Kisame returned, well into the night, to find that Itachi had claimed every single piece of fabric, made a nest, curled himself in it and tried not to act like he was scared of the fluid leaking out of his ass. Well, at least that answered the mist-nin's question of what secondary gender Itachi now had.

In his bad, he had brought food, medicine for pain and headaches, lubricant and plenty of hydrating fluids, like teas and bottled cold spring water. Luckily for Itachi, he was most unaffected by the strong scent of heat from the boy as he was simply far too young for Kisame to be interested in whatsoever.

"Looks like you presented as an Omega, Itachi," he offered and held up his bounty, "I brought you provisions."

An angry groan was all he got in reply, which caused him to inwardly chuckle.

Kisame knew what it was like to present, though he at least knew what to expect. Itachi did not, although it also could've been that he simply didn't _want_ Kisame to know.

He set the drinks down outside of the nest of blankets and towels, as well as the snack packs designed for heats and ruts alike, the lubricant (which he figured probably wasn't needed now he knew that Itachi was an Omega, but set down anyway) and the medicine for pain.

"I booked another room, so you'll be alone for this-" Kisame began to say, but Itachi looked up at him, and for the first time, he looked _vulnerable._

"Don't leave."

"Itachi, even if your heat scent doesn't affect me immediately, it will eventually," he offered seriously, "do you _really_ want to spend your first heat with someone like me? Not to mention I'd probably get you pregnant."

The boy didn't answer.

"Look, just…" Kisame sighed, and released his pheromones into the air, which caused Itachi to let out an involuntary moan of relief. It felt good.

"Be good for me and take care of yourself. I'll be right next door," the mist nin alpha commanded, and suddenly, Itachi felt as though he had to do exactly what Kisame said. Right now, it felt good…

But once his heat passed…

He would be having _words_ with the older man.

* * *

Three days passed, and Kisame woke up with a jolt that morning to see a pair of angry red eyes glaring at him.

The mist nin tensed immediately, his grip on the kunai he had under his pillow going from lax to tight in an instant.

"Itachi…?" he offered uncertainly. The other ninja smelt like smoke, fire, and a hint of something sweet and creamy…

"Don't. Ever. Alpha command me. Again," Itachi spoke each word with the hint of instant death on his tongue, and even Kisame couldn't help but quail under such an intense gaze.

"You know I only did that to protect you," he offered, and Itachi's eyes narrowed further. A moment of intense silence passed between the two as the young ninja realised that Kisame was telling the truth.

He had commanded him to take care of himself, which he might've otherwise not done, and might've sought out someone to _help_ him take care of himself. Kisame had protected him from himself, and others.

But he was still mad.

"Don't do it again."

"I promise."

Itachi got off him then, his scent strong and angry, and he was about to go back to his room before Kisame thought he heard a soft thank you.

But that couldn't have been right… could it?


	2. Chapter 2

It didn't take long for Itachi to go straight on suppressants due to his very first heat. He now understood why Kisame took them, and decided very quickly that he _did not like heats._

At least, he didn't like the vulnerability and the fact that he felt forced to masturbate for up to a week because of a bodily function. That, and now that he was _something,_ people could tell. People he honestly didn't _want_ to know.

Like Orochimaru, who upon realising he was an omega now, tried to do something to him that he honestly knew he wasn't going to like. Kisame had walked in on the near bloodbath with a _very_ pissed off Itachi and a very almost dead Orochimaru on the ground when he was 16, which caused his leave from the organisation.

It seemed as though Kisame's prediction of some alpha's (or in Orochimaru's case, a beta) certainly wanted to try and take advantage of an incredibly deadly ninja's secondary gender, but at the very least, Orochimaru was the last person who even tried. Everyone else was far too terrified of Itachi to try anything against him.

Not that anyone was particularly interested.

Everything fell into routine after that - Kisame had his yearly September rut, and Itachi followed after it with his yearly heat, and that continued solidly until the Uchiha was about to turn 18. At this point in their relationship, slowly but surely, the pair had begun to open up. Because of this, there was a mutual trust that began to blossom beyond that of a partnership.

Kisame told Itachi the truth about what happened to get him into the Akatsuki.

Itachi told him the full truth about the night of his clan's massacre.

And it was an even bigger sign of trust that Itachi told Kisame of his true allegiance, something that the mist ninja already assumed anyway, given what the Uchiha had told him about the massacre. It was to Itachi's great surprise that not only did Kisame completely accept it, but was also willing to play along with his plans. After all, Itachi had no desire to stop the 'world of truth' that Madara was proposing, though, he wondered if it was even possible to begin with.

Kisame didn't think so.

"Why would it matter?" he had offered one night, as they bathed together in a hot spring resort. It was one of the rare times where they had some time to just be themselves before a mission of chasing one of the tailed beasts. He was sitting against the rocks with a cloth on his navy blue hair, his muscular arms looped over two of the smaller rocks, his hands dipping the pool water, "it doesn't change my goals. It doesn't change yours. I don't particularly care what Pein wants to do. As long as you don't stab me in the back, then who you truly are is of no consequence."

Itachi remained silent as he sat on the side of the pool, a towel on his lap. It seemed as though he had not been prepared for his partner's reply, at all.

"So you plan to die."

"Yes," the Uchiha sighed, "I'd like to live, but I doubt I will. I can feel my body growing… sick."

"Sick?"

The omega nodded, "yeah. Every time I use my eyes, it gets worse. I know I'll only last a few more years… so I may as well do what I have to do before I leave."

It made more sense now, why Itachi was so very careful during his heats. Kisame knew that if he risked pregnancy, his sickness would be accelerated, and it was clear that the younger man had much to do before his body gave out. Not that he ever expected Itachi to take a partner, but he WAS a teenager, at the prime of his sexuality. It wouldn't have surprised the older man if he wanted to try it.

"Such is the life of a ninja, I guess…" The former mist nin merely took the cloth off of his head, dunked it in the water to reheat it, and placed it back on his head, "We don't live long. Most of us, anyway."

He was surprised that he was almost 30. He expected to be dead by now.

"Ah well…" Kisame sunk more into the water, and looked up at Itachi with a grin, "aren't you gonna get in?"

The Uchiha blinked, looked at him, and then looked away with a slight flush to his cheeks that Kisame suspected was not due to the hot water.

"What's up? Suddenly body shy around lil' old me?"

"Shut up," Itachi slipped into the water, stubbornly looking away from him, which caused Kisame to giggle. As the young man settled into the water, the mist nin had to snicker once more.

"I can't believe they partnered me with a pacifist."

"I can't believe they partnered me with a nihilist."

The older man snorted at that. He supposed he was. Then again, Itachi had trusted him with his secrets, and he with his. He supposed if they turned on one another, they'd just have to kill each other.

How nihilistic was _that?_

"So we're incompatible belief wise - doesn't mean I don't respect you completely," the blue skinned man smiled over at Itachi, who met his gaze, his eyes black for a rare change. Most of the time, his Sharingan was permanently activated - Kisame was one of the few of whom he didn't mind not having his genjutsu inactive around.

"Hn."

They remained silent for a while, just enjoying the hot water and the comfort it provided. It was almost summer, but in the cold north, it never really mattered much - it was always far colder.

"Hey, Kisame…"

"Hmm?"

"Have you ever shared your rut with anyone?"

It might've seemed like it came out of nowhere, but Kisame knew better. Occasionally, Itachi would fire questions at him about their secondary genders, so the older man merely shrugged.

"Yeah, a couple of times, but it's not really wise," when the Uchiha looked at him with an enquiring gaze, Kisame looked rather serious, "remember what I told you about Kiri-Alpha's being really savage, compared to the average alpha?"

"Yeah?"

"Well, my clan in particular is even worse," the missing-nin steepled his fingers, "it has to do with my Kekkei Genkai."

"Kekkei Genkai? You?" This was the first that Itachi had heard of it, though he supposed it was fairly obvious. Kisame didn't exactly look 'normal'.

"It was said that my ancestors of the Hoshigaki clan once begged for power from Poseidon, the god of the ocean," he explained, "and when the test was passed, Poseidon granted the clan power in exchange for their humanity," the ninja pointed to his skin, "blue skin, gills, and a specific appearance that looked akin to a type of shark was the Kekkei Genkai that was passed down through my clan. Due to its terrifying nature, it evaded the purge Kirigakure enforced," Kisame snorted, "not like they would've done anything anyway - we're not exactly easy to cut down."

Itachi remained silent as the other ninja explained, "anyway. Just like the Uchiha clan in that it produces very powerful Alpha's and Omegas, the Hoshigaki clan produces as much too. I wouldn't want to expose anyone who wasn't strong enough to be able to handle me in rut. I could kill them, and that's not so fun in the bedroom."

"I suppose not," Itachi commented softly before they lapsed into silence once more.

But the next question caught the former mist nin off guard, "so would _I_ be able to handle you?"

"Wh-" the older man blinked. It was true that Itachi was a powerful ninja, and also a very powerful Omega. All he needed to do was release his pheromones in the room and have a hoard of Alpha's (and even betas) ready to do as he commanded without even a blink of his Sharingan. In theory, he would be able to.

But…

"Are you asking to share my rut with me?" Kisame looked pretty surprised.

Itachi shrugged, "you're the only alpha I honestly trust. And I don't really want to die a virgin."

"That's all well and good, but," Kisame was honestly rather taken aback. Itachi was also a very attractive man, to the point of gender ambiguity that many men mistook him for a woman, and those that did not, who wanted his attention. But it had seemed that Itachi had no interest in either - except for him.

But he was also a lot older than Itachi. He had watched the boy grow up, after all, so it felt a bit weird to want to be intimate with someone who for all intents and purposes still kind of… seemed like a child.

Kisame was a man of morals, even for an S ranked ninja who had massacred hundreds.

"Are you _sure_ this is what you want?" the older ninja asked.

Itachi nodded, his face serious. It was clear he wanted this.

The mist-nin could only sigh, "alright. We'll sync our rut and heat together so we can get the medicine for it beforehand."

After all, he had no intentions of knocking Itachi up.

Months later, they had had their shots, and then shared their respective heat and rut together. It was fun, Kisame had to admit, and once they had both calmed down from the first day high that always occurred when their hormones spiked, they had even tried out some funky things, such as seeing if Itachi's sharingan could inflict pleasure as well as pain.

Turned out it could. Itachi made Kisame swear not to tell a soul.

He did not.

Years later, they had eventually passed on. The pair met in the Afterlife, a place of peace and tranquility. For a while, it was as though they were alone… but eventually, their souls called to one another, and they met once more.

"And here I thought I would be on the way to fire and brimstone," Kisame remarked with a smile.

"I'm glad to see you," Itachi responded with a rare smile.

They walked together through the glowing fields. It was bright sometimes, and calm all the same.

"Say, if we reincarnate, should we actually come back as a weasel and a shark?"

"But then how would we meet again?"

"Well… I could eat you."

"That's gross."

"Well I know you taste good- OKAY HAVE MERCY!"

Their laughter filled the void, and the fields grew brighter.


End file.
